Scripting
I've run into this problem twice now and it drove me nuts: If you define a label, and have a comment on the same line as the label, the label will not be found by the interpreter! ie:
My_Label: 'This is my label
If you then reference My_Label in the script, you will get an error telling you that the is no label call My_Label, even though you know it's there. I hope this helps someone...